Every November, it’s a now familiar sight. Hordes of shoppers camped out on the Friday after Thanksgiving, wrapped up in sleeping bags waiting to get 80% off a 42-in. TV, perhaps, or four pairs of jeans for the price of one. This year, those lines are likely to start even earlier, when dinner is barely cold at 8 p.m. on Thursday. Clearly, something sets apart those willing to ditch loved ones in search of a sale while the rest of us lie slumped in front of a movie rerun in a tryptophan torpor.

As it turns out, a passion for finding bargains is genetically preprogrammed in all humans, although it’s activated much more in some than others. Spotting special offers triggers a release of dopamine, the feel-good neurotransmitter that I like to think of as buyagra. Dopamine is such a powerful chemical that our brains have developed a built-in system to clean it up as quickly as possible. One in four Caucasians has an otherwise harmless flaw in what’s known as the COMT gene. While the rest of us can flush our brains free of dopamine with the efficiency of a Dyson, those with an iffy COMT gene can brandish only a hand broom. It takes more time and effort to flush their brains clean of buyagra — and so they are physiologically more prone to splurge, especially on bargains.

The minute one of these bargain addicts sees one “Sale” sign — cue a jolt of dopamine — they’re hooked; before it can be cleared away, the dopamine’s already triggered a second reaction to another clearance rack and so on. It works much like any intoxicant: the more deals they experience, the more they crave. It’s easy to identify who those men and women might be in our lives. They like to go to discounters like T.J. Maxx or Marshall’s, not in search of any one particular item but simply to get a big markdown on something. Ironically, bargain hunters might wind up with a closet full of useless stuff and large credit-card bills, which they might justify because the individual purchases themselves weren’t that big.

Of course, a propensity for bargain hunting isn’t purely genetic. Mine started with my own mother, a Scot who proudly embodies her nation’s renowned thriftiness. (Sample joke: Tip for saving gas — push your car to the destination and invariably passersby will think you’ve broken down, volunteering to help). Many hardcore coupon cutters I’ve interviewed cite hardscrabble childhoods or food-bank visits as the foundation of their frugality. Certainly, in the past decade, deal hunting has gone from a sign of indigence to one of intelligence; thanks to the roiling economy and an uncertain future, more people have migrated to the markdown section than ever before. Add to that the fact that eBay has taught us that prices weren’t fixed by the great printer in the sky. Internet-equipped smartphones turned price comparison into a one-step process in your palm — the practice known as showrooming that’s so detested by retailers. But in our search for bargains, we would do well to ask ourselves whether we are really trying to economize or whether we’re being driven by an even stronger impulse: the chemical drive to get a good price.

Mark Ellwood has written regularly for the Financial Times Weekend and How To Spend It Magazine, T: New York Times style magazine, Wall Street Journal Weekend, Bloomberg Business Week and Departures among others. The views expressed are solely his own.

Ellwood is the author of Bargain Fever: How to Shop in a Discounted World.